// 云函数入口文件
const cloud = require('wx-server-sdk')

cloud.init()
const db = cloud.database()
const _ = db.command
const $ = _.aggregate
// 云函数入口函数
exports.main = async (event, context) => {
  return await db.collection("chat")
  .aggregate()
  .project({
    _id: 1,
    _openid:1,
    content:1, 
    createtime:1,
    time:1,
    to_openid: 1
  })
  .sort({
    createtime: -1
  })
  .lookup({
    from: 'users',
    localField: '_openid',
    foreignField: '_openid',
    as: 'sendedBy',
  })
  .match(_.or([
  {_openid: event._openid},
  {to_openid: event._openid}
  ]))
  .skip(event.skiplength)
  .limit(30)
  .end()
}